Re: how to allow integer overflow for calculating hash code of a string?

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От Craig James
Тема Re: how to allow integer overflow for calculating hash code of a string?
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Msg-id CAFwQ8rcdk68h5kC+77VdPqwPmju3KD1BTkm6Sh4_YYEzcBwcwA@mail.gmail.com
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Ответ на how to allow integer overflow for calculating hash code of a string?  (Haifeng Liu <liuhaifeng@live.com>)
Ответы Re: how to allow integer overflow for calculating hash code of a string?  (Haifeng Liu <liuhaifeng@live.com>)
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On Thu, Sep 20, 2012 at 1:55 AM, Haifeng Liu <liuhaifeng@live.com> wrote:
I want to write a hash function which acts as String.hashCode() in java: hash = hash * 31 + s.charAt(i)... but I got integer out of range error. How can I avoid this? I saw java do not care overflow of int, it just make the result negative.


Use the bitwise AND operator to mask the hash value with 0x3FFFFFF before each iteration:

  hash = (hash & 67108863) * 31 + s.charAt(i);

Craig

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